Ascorbic acid (chemical formula C6H8O6) is used commercially to neutralize bleach in water storage tanks. Bleach, which is added to water tanks as a disinfectant, needs to be completely eliminated before the water is fit for drinking or agricultural purposes. Ascorbic acid neutralizes all residual bleach in a matter of seconds, and 1/4 tsp. of the substance added to 1 gallon of water effectively removes all traces of bleach.

So I will be using 50/50 bleach, some TSP, brush with a 3M doodlebug,let sit min or two, rinse, garden sprayer to neutralize, rinse with wimpy pressure washer.